1. Field of the Invention
This invention relates to a process and apparatus for combustion of a mixture of fuel and oxidant, said oxidant preferably being 100% oxygen, suitable for use in high temperature furnaces, such as glass melters.
2. Description of the Prior Art
In order to meet the requirements for use in high temperature furnaces, such as glass melters, an oxygen/fuel burner must be efficient, cost-effective, and maintenance-free, all the while producing low pollutant emissions. Use of a burner system for oxygen/fuel combustion which is not suitable for use in high temperature furnaces can result in excessive flame temperatures or improper flame shapes within the furnace, leading to furnace refractory and burner damage, and high emissions of NO.sub.x, SO.sub.x, particulates and batch volatiles, often exceeding the maximum levels permitted by government regulations. In addition, the cost of operation of such high temperature furnaces can be dramatically effected by burner firing performance, firing interruptions, burner influence on product quality, burner system maintenance and service requirements, and finally on the cost of the burner system itself.
In traditional oxy-fuel burners, the design of the burner nozzle configuration, including flow velocities of both oxygen and fuel, orifice size, geometry and distance between fuel and oxygen streams, turbulence considerations, aerodynamic shaping at flow exits, and selection of appropriate nozzle materials, is carefully considered to yield combustion process and flame characteristics necessary for heating the furnace interior. An example of such a device and process are taught by U.S. Pat. No. 5,199,866 which teaches an oxy-fuel system including a self-cooled adjustable oxy-fuel burner which produces a luminous flame having a concentric, fuel-rich phase and an outer surrounding oxidizer-rich phase and where the flame generated by the system is directed through a burner block (pre-combustor) mounted on the flame end of the burner, the burner block having a length-to-diameter ratio fixed by the firing rate of the burner. Similarly, U.S. Pat. No. 4,690,635 teaches a high temperature burner having a fuel nozzle disposed within an oxygen conduit and disposed external to a burner block to which it is secured. Gaseous fuel flows through the nozzle and mixes with the oxygen from the oxygen conduit to form a sustainable flame substantially within the refractory burner block.
U.S. Pat. No. 2,360,548 teaches a method and burner for combustion of a hydrocarbon fuel such as natural gas to produce a luminous flame consisting of a central fuel nozzle disposed within an air duct which, in turn, is disposed within a burner block. Air from the air duct flows around the fuel nozzle and mixes with the fuel in the burner block. The end of the fuel nozzle is enlarged to form a venturi between the fuel nozzle and the air duct in order to increase the velocity of the air flowing into the burner block.
U.S. Pat. No. 4,439,137 teaches a method and apparatus for combustion in which air is injected into a furnace through a burner tile in a deviated flow pattern asymmetrical with respect to the burner tile and mixed with fuel introduced into the burner tile through a nozzle disposed in the burner tile. A second portion of air is introduced into the combustion chamber downstream of the burner for completion of the combustion process. Contrary to this invention, the burner disclosed by the '137 Patent is designed to prevent the formation of soot.
U.S. Pat. No. 5,209,656 teaches a combustion system for high velocity gas injection in which a fuel or oxidant is injected at high velocity through a nozzle recessed in a burner block and a purge gas having the same composition as the gas injected through the nozzle is injected at a low velocity through the burner block and around the nozzle into a combustion chamber in a defined relationship such that the low velocity gas forms a protective barrier to combustion zone damage due to the flow dynamics caused by the high velocity gas.
U.S. Pat. No. 4,541,796 teaches a process and apparatus for firing a furnace using oxygen or oxygen-enriched air in which the oxygen or oxygen-enriched air is injected into the furnace through a plurality of jets surrounding a central fuel jet at a velocity sufficient to cause aspiration of furnace gases into the oxygen or oxygen-enriched air jets before they mix with the fuel jet. The fuel nozzle of the disclosed burner extends through the combustion chamber wall and is flush with the inside of the combustion chamber wall.
U.S. Pat. Nos. 4,717,334, 4,797,087, and 4,515,553 generally teach burners in which the fuel nozzle is disposed external to the burner block to which the burner is secured. U.S. Pat. No. 4,473,350 teaches an oxy-fuel burner having a combustion chamber recessed into a graphite burner block where the fuel is supplied to the walls of the combustion chamber for film cooling and where the burner block includes a plurality of parallel cooling bores arranged in an array about the combustion chamber so as to reduce the temperature of the burner block and the combustion chamber.
Crucial to the performance of an oxy-fuel burner in high temperature furnaces are flow velocities, firing rates and burner block design. Improper selection of flow velocities, firing rates and/or burner block cavity design can lead to a high temperature flame within the burner block and vicinity of the oxy-fuel burner nozzles and, thus, generally leads to deterioration/oxidation of burner nozzles; damage to burner block refractory material which can affect the normal flame direction within the burner block cavity; undesirable heating of furnace walls, not only affecting the life expectancy of such walls, but also effecting an increase in heat loss to the areas surrounding the furnace; non-luminous and short flame coupled with non-uniform heat distribution to the load; decreased productivity and poor product quality; and lower burner nozzle and burner block life, as well as increased maintenance.